Nuclear magnetic resonance (NMR) is the name given to a physical resonance phenomenon involving the observation of specific quantum mechanical magnetic properties of an atomic nucleus in the presence of an applied, external magnetic field. Many scientific techniques exploit NMR phenomena to study molecular physics, crystals and non-crystalline materials through NMR spectroscopy. NMR is also routinely used in advanced medical imaging techniques, such as in magnetic resonance imaging (MRI).
A superconducting quantum interference device (SQUID) is a sensitive detector which is used to measure extremely weak magnetic signals, such as subtle changes in the human body's electromagnetic energy field based on the quantum mechanical Josephson effect. A Josephson junction is made up of two superconductors, separated by an insulating layer so thin that superconducting electrons can tunnel through. A SQUID consists of tiny loops of superconductors employing Josephson junctions to achieve superposition: each electron moves simultaneously in both directions. Because the current is moving in two opposite directions, the electrons have the ability to perform as qubits (that theoretically could be used to enable quantum computing). SQUIDs have been used for a variety of testing purposes that demand extreme sensitivity, including engineering, medical, and geological equipment.
Both the low-field NMR and MRI are based on SQUID, which can avoid the drawbacks of high-field NMR and MRI such as susceptibility artifacts, the cost issue, the size and complexity of the high-field system and so on. The demand of the field homogeneity is not as strict as that of high-field NMR/MRI although the signal-to-noise ratio (SNR) is weak in low field NMR/MRI. Homogeneity of 1 part per 104 in the magnetic field can reach a line width of 0.426 Hz in the NMR spectrum. Therefore, the construction of a low-field spectrometer of high spectral resolution is much easier than that of the high-field NMR/MRI.
Nuclear magnetic resonance imaging (MRI) is a clinical diagnostic tool which is based on the difference in longitudinal (T1−1) or transverse (T2−1) relaxation rates of protons in different tissues. In other words, it is important to study the change of spin-lattice relaxation time T1, spin-spin relaxation time T2 and effective relaxation time T2* for medical diagnosis. However, it is still a little complicated and inconvenient to use so many parameters and make images for diagnosis.
Currently, the main method of distinguishing between normal tissue and tumor tissue depends on pathological analysis of specimen obtained from biopsy. Such examination demands high human resource as this requires professional pathologists and it takes time. Moreover, when the quantity of specimen is undersized, there is usually insufficient amount to conduct all the examinations. Therefore, pieces of specimen needs to be used for regular microscopic examination under H&E staining and many other immunohistochemical staining simultaneously for coming to diagnosis. Furthermore, the specimens are depleted and unable to be used in follow-up pathological examinations.